This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast milk is considered the nutrition of choice for infants, including premature infants in the Neonatal ICU (NICU). In the case of very low birth weight (VLBW) infants, this milk is generally supplemented with a human milk fortifier (HMF) in order to provide the additional nutrients that these babies require. We propose to investigate a HMF made from pasteurized donor human milk, in particular regarding calcium absorption, growth, bone mineral status, body composition, and feeding tolerance. We hypothesize that these study parameters will result in adequate outcomes with the use of the donor milk based HMF. The use of a human milk fortifier made from pasteurized donor human milk will provide adequate calcium absorption to preterm infants. In addition, this new fortifier will provide adequate growth and bone mineralization. Primary Aim: To determine calcium absorption in premature infants fed mother''s own milk fortified with pasteurized donor human milk fortifier. Secondary Aims: (1) To evaluate the growth, bone mineral status, and body composition of premature infants fed mother''s own milk fortified with pasteurized donor human milk fortifier, and, (2) To assess feeding tolerance (pilot data) in infants fed mother''s own milk fortified with pasteurized donor human milk.